1. Field of the Invention
The present invention relates generally to a shearing machine, and more specifically to a shearing machine used to cut off material being continuously fed into predetermined lengths.
2. Description of the Prior Art
In an electric-welded tube manufacturing installation which can mass-produce, for instance, relatively thin-walled and relatively small-diameter electric welded tubes, there is generally a shearing machine at the last manufacturing stage which can cut a material into predetermined dimensions while the material is being continuously fed in a straight line.
As the above-mentioned shearing machine, a scotch-yoke type is well known, in which a rotating arm is used to move a movable cutter downward to cut off a material and to move a pair of fixed and movable cutters horizontally. In this case, it is necessary to synchronize the horizontal speed of the cutters with the horizontal speed of the material to be cut at least during the cutting period, in order to prevent the cutters from being broken.
In such a shearing machine, however, since the circular motion of the rotating arm is not constant in the horizontal direction speed, it is necessary to adjust the revolution speed of the driving motor at short time intervals by using an appropriate speed adjusting device. In order to achieve sufficiently accurate speed control, it is necessary to use a motor with relatively large capacitance ratings.
Additionally, in this case, there exist some functional limitations such as the cutting depth and the length of material to be cut.
To overcome these problems, another shearing machine has been employed in which a double-acting hydraulic cylinder device controlled independently by electromagnetic valves is used for moving the movable cutter downward to cut off the work material. In this shearing machine, however, since the electromagnetic valves entail a response delay, when the material to be cut is fed at a high speed, it is practically impossible to cut the material accurately into an appropriate length.
A more detailed description of the representative prior-art shearing machine will be made with reference to the attached drawing under DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS.